Radial excitations of qq− and non-qq− candidates

Nuclear Physics B (Proc. SuppI.) 74 (1999) 171-179

&dial

excitations

PROCEEDtNGS SUPPLEMENTS

of qq mesons and non-qq candidates

L. Montaneta “CERN, Geneva, Switzerland Some recent experimental observations made on the meson spectrum are discussed, with particular attention to qq radial excitations and to possible non-qq states. This review is mainly based on analyses of proton-antiproton annihilations at low energy. For a more complete review, see the 1998 edition of the Review of Particle Physics.

1.

INTRODUCTION

It is well known that the Constituent Quark Model (CQM) and SU3, limiting ourself to three flavours (u, d, s), provides a simple framework for the interpretation of the hadron spectrum. In this model, mesons with a given set of quantum numbers JPC appear in nonets (8+1). CQM restricts the sets of allowed Jpc quantum numbers to O-+ (PS), I-- (V), 0++ (S), l++ (AV), l+- (AV’), 2++ (T), etc. Several of these nonets are well established [l]. A striking example is provided by the 2++ nonet with a2 (1320)) fs (1270), P2(1525) and K$ (1430) [2]. The 19 measured decay modes -+ PS + V) of these 2++ states (T-+2PSandT are found to be in good agreement with SU3 once the non-point-like nature of the states has been taken into account (using the Blatt-Weisskopf angular momentum barrier factors with R = 0.2 fm). The octet-singlet mixing angles of the PS, V and T nonets, left as free parameters of the fit, are in excellent agreement with other, independent, determinations of these angles: - 15’) 37” and 28”, for the PS, V and T nonet, respectively. According to CQM, mesons, made of one quark-antiquark pair, should not appear with Jpc = O--, O+-, l-+, 2+-, etc. For more than thirty years, states with these ‘exotic’ quantum numbers have been looked for. In 1998, conspicuous evidence for a l-+ state has been obtained [3, 4). It wiil be discussed in Section 3. CQM allows for an interesting possible extension of the meson spectrum: each nonet (2s+1)L~ may appear, in addition to its ‘ground state’ n = 1 (“+‘)LJ, with various levels of ‘radial excita0920-5632/99/$ - see frontmatterQ 1999 Elsevier Science B.V. PI1 SO920-5632(99)00157-7

tion’ (n = 2, 3... ..).

These levels are well known in the heavy-quark sector; i.e. \k (3097), \k (3685), @ (4040) - the ground state, first and second radial excitation of the Jpc = l-- charmonium, respectively -and Y (9460), Y (10023), Y (10355) Y (10580) for the bottonium. We discuss the radial excitations for the light quark mesons in Section 4. Ten years ago, S. Godfrey and N. Isgur [5] gave a beautiful and comprehensive interpretation of the meson spectrum, using CQM with a minimal number of parameters. It will be used as a reference to underline how the experimental results obtained during the last ten years may affect or complete this picture. In meson spectroscopy, the scalars and pseudoscalars deserve particular attention. They will be discussed in Section 5. 2. PROTON-ANTIPROTON STATES

INITIAL

Proton-antiproton annihilations at low energy occur in a limited number of initial states. These limitations have important practical consequences, as they allow for detailed partial waveamplitude analyses of the final states, for example the analysis of three-body annihilation Dalitz plots, with a limited number of parameters. Annihilations at low energy (say with an incident antiproton momentum less than 200 MeV/c) occur essentially from S and P states of the protonium. The P/S ratio depends on the hydrogen target density as the Stark effect which controls the P + S transitions is more effective with high densities. The OBELIX collaboration (hereafter referred to as OB) makes use of this fact by comparing the results obtained for a given final state All rights reserved.

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L. Montanet/Nuclear

Physics B (Proc. Suppl.) 74 (1999) 171-l 79

with three different target densities [6]. It can be shown [7] that 90% of annihilations at rest in liquid hydrogen occur from S states (‘SO and 3S1) whereas this fraction goes down to 20% for a low pressure gas target. Note that for annihilations at rest in liquid hydrogen, the discrimination between the two dominant initial states ‘SO and 3Si is possible when the C-parity of the final state is known. This is the case for annihilations into n y. Annihilations at rest in liquid hydrogen being dominated by S states and phase space being limited to a total energy of 1.876 GeV, the production of scalar and pseudoscalar mesons with limited orbital angular momentum is expected to be dominant. More precisely, most of the twobody annihilation channels will be of the form:

‘Se

3S1

+ a0 + x (77)

(I)

+ fo + 7r (rl)

(2)

-+ n*(q*)

(3)

+ g

+ bi + n (77)

(4)

-+ hi + r (77)

(5)

-+ W(P) + g

(6)

where au; fe; br; hr; w and p stand for any state with I, Jpc = 1, Off; 0, Cl++; 1, If-; 0, l+-; 0, l-and 1, l--, respectively, 7r* and r]* stand for any excited state of the n and q mesons, respectively, and 0 stands for the low-mass 7r7~S-wave (see Section 5). Reactions (l), (2) and (3) have been extensively investigated by the Crystal Barrel collaboration (hereafter referred to as CB).

OF 3. OBSERVATION STATE (Jpc = l-+)

AN

EXOTIC

One of the first claims for the observation of a resonant P-wave in the 177~system was made by Alde et al. (GAMS) (81. They observed a resonant l-+ wave with M = 1405 Z!Z20 MeV and P = 180 f 20 MeV. An important characteristic of the reaction studied by GAMS was the dominant a2 (1320) production which, through interference effects, reveals the presence of an r]rr P-wave. More recently, similar experiments performed at IHEP [9], KEK (lo] and BNL [4] have led to similar conclusions (The mass and width

observed at BNL are M = 1370 f 16 f 40 MeV and l? = 385 f 40 f 80 MeV, respectively.) CB [3] has analysed the annihilations at rest in deuterium: pn --) r]w-no

.

(7)

Two initial states contribute: 3Si (66%) and ‘Pi (34%) (Note that with a liquid deuterium target, P/S may be large Ill].) Only two ‘known’ final states may contribute: p-77 and a27r. Other final states (like ae7r) are forbidden by J,P,C conservation. One finds a large contribution (57%) of the p-n channel and a less important but significant contribution of the asn channel (15%). In addition, one needs to introduce an exotic l-+ 7x resonance (15%). This resonance interferes strongly with the two other channels. These interferences provide a precise determination of the mass and width of the exotic resonance: M = 1400 f 30 MeV ,

I? = 310 5 70 MeV .

Note that, here, the exotic resonance production is comparable to a2 (1320) production (considering only the 7~ decay mode of both resonances). Current interpretations of the l-+ state in terms of a ‘hybrid’ meson (with constituent quarks and gluons; for a review, see [12]) or in terms of a ‘multiquark’ meson, do not favour a dominant qn decay mode. On the contrary, Ref. (131 suggests that a l-+ hybrid meson, with a mass of 1500 MeV and a width of 280 MeV, could decay into 71~ via the U(1) anomaly. With an octet-singlet mixing angle of 17”, one gets for this ‘hybrid’ a substantial qx decay mode, as well as $n. Other decay modes are also expected: pr, bir, frr. It is now an interesting challenge to look for these decay modes. 4. RADIAL

EXCITATIONS

OF THE qq

MESONS 4.1. p (1450) The analysis pn -+ n-

and p (1700) of the reaction 27r” [14]

(8)

shows that it is dominated by the production of p-mesons decaying into 2x with the following masses and widths:

173

L. Montanet/Nuclear Physics B (Pmt. Suppl.) 74 (1999) 171-I 79

M 763.7 k 3.2 MeV 1410 f 13 MeV 1780 zt 40 MeV

r 152.8 f 4.5 MeV 343 f 25 MeV 275 f 50 MeV .

4.3. a2 (1650) and f2 (1640) CB has reported [18] an analysis of the threebody annihilations pp+27l+?r.

There is no need for an additional p around 1300 MeV as suggested by other analyses of 3x annihilations and by the analysis of the 3n decay of J/*. The masses and widths observed for p (1450) and p (1700) are in remarkable agreement with the values obtained from the analyses of e+eannihilation data (151. These p (1450) and p (1700) are logically associated to the first radial excitation (2 3Si) of p (770) and to the isovector member of the 3Di qq nonet, respectively [5]. The 2x decay of p (1450) is not the dominant decay mode of this resonance, which is: p (1450) --) p (770) + d .

(9)

Note that (9) is of the type: R* --+ R+O++

(10)

where R and R* have the same quantum numbers. Not surprisingly, this transition plays a particular role in the radial-excitation decays. Other concrete examples of this transition are provided by the *I* and Y* decays. According to the 3Pc model predictions of the BCPS collaboration [16], the decay modes observed for p (1450) and p (1700) provide strong evidence that these two resonances are the I = 1 members of the 2 3Si and 1 3Di qq nonets, re spectively. 4.2. w (1420) This state has been observed in efe- annihilations. Two decay modes have been identified: w+ --+ pn and w* + wg’, the last one being also observed in proton-antiproton annihilations [17]. The w (1420) is interpreted as the partner of the p (1450), i.e. as one of the two I = 0 members of the 2 3Si qq nonet. The masses and decay modes of p (1450) and of w (1420) suggest that the octet-singlet mixing angle of this nonet is close to ‘ideal’.

(11)

Looking for higher mass states, we have to analyse data obtained with an incoming antiproton momentum in the range 1 to 2 GeV. Thii is done at the expense of the introduction of a larger number of contributing initial states. However, the analysis of reaction (11) provides clear evidence for a 2++ resonance with the decay mode 82+7+7r.

(12)

The mass and width of this a2 are M = 1650 f 40 MeV, I’ = 280 zt 50 MeV . Searches for other decay modes are in progress. This a2 (1650) can reasonably be interpreted as the first radial excitation of a2 (1320). Moreover, an fs 1640 has been observed in several reactions [19, 201 including antiproton-neutron annihilations [21], with ww and fsa decay modes. This fs (1640) may be interpreted as the isoscalar partner of as (1650) in the 2 3P2 qq nonet. 4.4. al (1640) CB has analysed the four-body

annihilations

[221 pp + 47r* .

(13)

This reaction is dominated by annihilations into 20, cr + f2, 2f2, and 7r2 (1670) + K. In addition, one needs to introduce a new resonance: pp --) ai (1640) f #

(14)

with al (1640) ---) u + ~T’,u --) 2n0 and ai (1640) + f2 + x0, f2 -+ 27r0. Note that the 47r” final state cannot provide information on other possible decay modes such as al (1640) -+ al (1260) + fl, or al (1640) --) p + lr.

This last decay mode has been observed by DELPHI (231 in the analysis of the 7 decay: I- --+ 37r+ u. The mass and width obtained for this al (1640) are M=1640&25MeV,

l?=300&50MeV,

L. Montanet/Nuclear Physics B (Proc. Suppl.) 74 (1999) 171-179

174

which make it a good candidate excitation of al (1260).

for the first radial

4.5. General remarks on radial excitations Limiting ourselves to the isovector sector of the light-quark spectroscopy, and postponing the discussion on the scalars and pseudoscalars to the next section, one sees from the above discussion that most of the first radial excitations of the S and P qq states have been identified in recent experiments on meson spectroscopy. The identification of the first radial excitation of br (1235) requests the analysis of pp annihilations into 77r, a channel which has not yet been analysed systematically. Preliminary results [24] suggest the presence of a resonance, br (1700), which could be a manifestation of the isovector member of the 2 ‘Pr qq nonet in the reaction: Pp

-+

br (1700)

+ 7r,

bi (1700) -+ bi (1235)

I’(KK)/I-‘(n7r) + CT,

bi (1235) + w + 7.r Note that p (1450) is heavier than the isovector members of the 1 ‘PI, 1 3Pr and 1 3Pz qq nonets whereas the radial excitations of al (1260) and a2 (1320), with masses around 1650 MeV, are slightly lighter than the known 13Di, 13D3 and 11D2 isovector states, which have masses in the range 1670 to 1700 MeV. The predictions of Godfrey and Isgur (51 were, for the mass of the isovector members of the 2 3Sr, 2 ‘Pi, 2 3Pr and 2 3P~ q4 nonets, M = 1.45, 1.78, 1.82 and 1.82 GeV, respectively. The last three predictions seem to be overestimated by 100 to 200 MeV, an indication that the confining potential used in Ref. [5] may not be optimal for these light-quark states. 5. THE SCALARS SCALARS 0-+

O++ AND

PSEUDO-

5.1. The scalars The scalars are particularly difficult to identify. The reactions in which they are usually studied are the S-wave two-body decays: o++ -+ o-+

+ o-+

Important threshold effects (KK, ~7r,~‘fl...) may obscure the resonant behaviour of the system [25]. Moreover, in addition to the qq states, several ‘exotics’, i.e. multiquark states, ‘KK molecules’ 1261, ‘deusons’ 1271, and ‘glueballs’ [28], are expected to occur within the 1 to 2 GeV mass range. Let us first consider the I = 1 sector (%).Two resonances have been observed: the well known aa (980), first observed as a KK ‘threshold enhancement’ associated to a scalar resonance observed in the qn system, and, more recently, the The aa (1450), observed in pp annihilations. a0 (980) lies very close to the KK threshold and couples strongly to this channel. These features have been underlined in support of the ‘KK molecule’ interpretation of a0 (980). But a recent analysis of pp annihilations at rest, reaction (16), [29] gives a relative branching ratio for a~ (980):

.

(15)

= 1.03 f 0.14

and the width determined from the T-matrix pole is 92 f 8 MeV. These results suggest that the wave function of a~ (980) includes an intrinsic qq component along with the KK molecule component . The a~ (1450) has been observed in pp annihilations by CB [29] and OB [30]. CB has observed an a~ in three decay modes with branching ratios which agree quite well with SU3 predictions, as can be seen in the following: -+ % su3

Kit 0.88 f 0.23 0.69

I /

v7” 1

/

1

I / /

rl’r 0.35 f 0.05 0.39

OB has studied the KK decay mode and also finds it necessary to introduce an ae in addition to a~ (980), to obtain an acceptable fit of the three-body annihilations: pp -+ K’K-r+

(16)

However, OB compares the results obtained with various densities of the hydrogen target, and shows that O++ resonances are produced from lS0 pp annihilations whereas 2++ mesons, like a2 (1320), are mainly produced from P states. CB assumes that the initial state is purely ‘So. It may partly explain the differences in mass and width assigned by these two experiments to 80:

L. Montanet/Nuclear Physics B (Prvc. Suppl.) 74 (1999)171-I79

M 1480 f 30 MeV 1290 f 30 MeV

r 260 f 15 MeV [29] 80 f 5 MeV [30] .

Further analyses are necessary before a precise mass determination can be given, but there is no doubt that an I = 0, Jpc = O++ resonance is observed in the 1300-1450 MeV mass range. Its decay properties make it a good candidate for an I = 1 3Ps qq state. Considering the masses of the 3Pr [ai (1260)] and 3P2 [a2 (1320)] states, it is a priori logical to associate this ac to the 3Ps qq ground state. If we adopt this interpretation for ae (1300-1450), ac, (980) can then be interpreted as an ‘exotic’ state (i.e. a non-qq state) although its wave function may still include a significant qq component. The first radial excitation of ac (1300-1450) could then be expected to occur around 1700 MeV. Godfrey-Isgur (GI) [5] predicts a mass of 1.09 GeV for the I = 1 member of the 1 3Ps qq nonet and 1.78 GeV for the 2 3Pa: ac (1300-1450) falls in between these two predictions. The I = l/2, Jp = O+ spectrum (Kg states) has been recently reanalysed, using the K-matrix formalism, by A.V. Anisovich and A.V. Sarantsev (311who find two poles, at [1415 f 25 - i165 f 251 and at (1820 f 40 - i125 f 501, in good agreement with the results of the analysis made on the reference data [32]. It is natural to associate KG (1430) to the 1 3Pe qq nonet, whereas K: (1950) would be the I = l/2 member of the first radial excitation 2 3Pe qq nonet. GI [5] predicts masses of 1240 MeV and of 1890 MeV, respectively, for these two resonances. We therefore arrive at a simple interpretation of the isovector and isospinor O+ hadron spectrum: as (1300-1450), in particular if its mass turns out to be close to 1300 MeV, is a good candidate for the isovector member of the 1 3P~ qq nonet, Ki (1430) being the isospinor member of this nonet. As concerns the 2 3Pe qq nonet, we do not have yet clear evidence for the isovector member (which should occur around 1700 MeV), the isospinor being identified with Kz (1950). In this scenario, ac (980) appears to be an extra state. In contrast with the isovector and isospinor mesons, the identification of the isoscalar is com-

175

plicated by the presence of scalar ‘glueball( which are expected to have masses comparable to those of the 1 3Ps and 2 3Pa qq states and can mix with them. A detailed analysis of the couplings to the various available final states is then necessary to disentangle the qtj from the glueball states and to determine their mixing [33]. In the 1998 edition of HPP [l], the isoscalar Jpc = O++ resonances are listed under four separate entries: fe (400-1200), 6 (980), fs (1370) fa (1590). To these one should add the fJ (1710), whose spin is not yet defined, but for which there is growing evidence for the presence of two resonances under this entry: fs (1700) and fs (1710). Note that the main decay modes of this fo (1700) are KK and nn, suggesting the presence of Ss states. Concerning fs (400-1200), also called cr, a first remark is in order: its width is so large (hence its mass so badly defined) that one may ask if it is a ~7r S-wave amplitude resonance or if this pole, far away from the physical region, is rather due to left-hand cuts not appropriately taken into account. Indeed, some authors interpret cr as a TUTS-wave background due to p and f2 (1270) tchannel exchanges [34]. However, it is unlikely that these t-channel effects could explain the to tality of the o phenomenon. Partial wave analyses of the KA system do not yield, in general, a unique solution. Traditionally, one groups the solutions into two categories: the ‘up’ solutions, which favour the existence of a (T with a low mass (M N 700 MeV), and a narrow width (I’ m 150 MeV); and the ‘down’ solutions, which correspond to a slowly rising phase shift of the ~7r Swave, starting from XITthreshold, going through 90” around 1 GeV, and reaching 180” around 1.8 GeV [35]. Note that, at 1 GeV, (at the KK threshold), this TX S-wave phase shift exhibits in addition a jump of 180°, owing to fs (980). The superposition of a broad g and of a narrow fa (980) with similar masses results in the appearance of two maxima of the S-wave amplitude which may be wrongly taken as evidence for two Oc+ resonances, (E, c’).The ‘up’ solutions have their proponents [36], but these solutions do not provide an acceptable description of data on 7r”ro S-wave (where p (780) is absent).

L. Montanet/Nuclear Physics B (Proc. Suppl.) 74 (1999) 171-l 79

176

A broad cr can be interpreted in several ways. Let us simply note that this c often appears whenever some energy, around 1 GeV, is available (with IG, Jp = O+,O+) as in the transitions (lo), not obviously involving the constituent quarks of the interacting hadrons. The production and decay properties of ~7 suggest that it is a key object of &CD, being simultaneously related to the chiral partner of 7, n’ and to the gluonic field [24, 371. fe (980), like ac (980), is often interpreted as a KK molecule (261. However, its interpretation as the ss member of the 1 3Pc qq nonet has been advocated by several authors [31, 38, 391. According to N. Tornqvist [25], both the as (980) and the fc (980) could be unitarized remnants of strongly shifted qq states whose ‘bare’ masses are above 1300 MeV. fo (1370) is now a well-established resonance although its large width (200 to 500 MeV) and the nearby broad u make its identification difficult. Its coupling to 7~ is small, and the corresponding loop on the Argand plot has a small radius. However, the fc (1370) pole appears on the third Riemann sheet of the complex energy plane, in contrast to the (T. Considering only its mass, a straightforward interpretation of this fs (1370) is to take it as one of the two isoscalar members of the 1 3Pc qq nonet. However, its large 47r decay width (with an important (TO contribution) suggests that this qq state (mainly non-d) mixes with a Of+ glueball. The most comprehensive information on fc (1500) comes from CB, studying protonantiproton annihilations at rest [40], but fc (1500) has also been observed in other processes: pp annihilations in flight, J/$ radiative decays, ‘central production’ in proton-proton interactions. The first indications on a scalar resonance in this mass region were given by GAMS [41] studying the reaction F+p+2n+n.

(17)

The branching ratios observed for fa (1500) exclude an important ss component: I’(KK)/P(total)

= 0.044 5 0.021

The dominant to be

decay mode of fa (1500) appears

frJ (1500) --t 2a as one may expect for a scalar glueball according to the QCD sum rules developed by S. Narison and G. Veneziano [37]. To summarize, of the five I = 0, Jpc = O++ resonances observed below 2 GeV, [fc (1700) remains to be firmly established and its ss nature demonstrated], the simplest, perhaps too simple, interpretation one may suggest is that fs (1370) and fs (1700) are the two isoscalar members of the 1 3Pa qq nonet, and fe (1500) is (mainly) a glueball. Of course, this glueball can mix with the nearby scalar quarkonia. In this scenario, fs (980) and B (as well as ac (980) for the isovector sector) are left outside of the qq nonet classification. As discussed above, fs (980) and ao (980) could be the remnants of higher mass qq states, or could be interpreted as ‘KK molecules’. I have underlined before why the cr may fall outside a simple qq model. Other scenarios have been proposed [5, 33, 38, 391. Some of them consider that fc (980) and cr may be the two isoscalars of the 1 3Pc qq nonet whereas fc (1370) and fs (1500) [or fc (1700)] could be related to the 2 3Pc qq nonet. GI [5] predicts 1.09 GeV and 1.36 GeV masses for the I = 0 members of the 1 3Ps qq nonet for the non+ and ss states, respectively. The corresponding masses for the 2 3Pc nonet are 1.78 GeV and 1.99 GeV. The 1.09 GeV state, being a nonss state, cannot be associated with fc (980) and, conversely, the 1.36 GeV state cannot be associated with fs (1370). In any case, fs (1500) does not find a place in this relativized quark model. 5.2. The pseudoscalars The O-+ qq meson nonet (r, K, n, 7’) is well known for departing from the Gellman-Okubo mass relation; this behaviour of the pseudoscalars is related to their Goldstone boson nature and to the U(1) anomaly which ‘explains’ the higher mass of the 7’ [42]. This nonet being taken as the ground state 1 ‘So qq nonet, one may look for its first radial excitation in the 1 to 2 GeV mass region. As in the case of the O++ mesons, it is easier to start with the isovectors. Two heavy pions

L. Montanet/Nuclear Physics B (Pnx. Suppl.) 74 (1999) 171-I 79

have been observed: K (1300) and 7r (1800). They may represent the first (2 ‘SO) and the second (3 ‘SO) radial excitations of the n-meson. However, O-+ exotic mesons are expected to occur in the 1800 MeV mass region and one must analyse other features of these heavy pions to identify them without ambiguity. The radial excitations have nodes in their radial wave functions which modify their decay branching ratios as expected from the standard SU3 relations.[43, 161. n (1300) has a large p1 decay, whereas its cr7r decay is relatively small, in agreement with the expectations of the 3Po model [16] for the first radial excitation of the r. K (1800) has, instead, a small pn decay whereas its CA decay is dominant. The 3Po model predicts for the second radial excitation of the 7~ a strong pw decay, whereas this decay mode should be small for a ‘hybrid’ (161. One heavy K, K (1460), is known. Together with x (1300), it suggests that the first radial excitation of the O-+ nonet is to be found in the 1300-1600 MeV mass region. q (1295) is a good candidate for the I = 0 non& member of this nonet (assuming that the two isoscalars of the nonet are ideally mixed). The mass of 77 (1295) is close to the A (1300) mass and its main decay mode is qu. In these conditions, one should expect for a standard q4 nonet, and ignoring possible mixing with other states, a second isoscalar (sS) in the 1500-1600 MeV mass region. Three experiments [44] have observed a KK* resonance, at 1475 f 20 MeV; it could be the ninth member of the 2 ‘SO q4 nonet. However, an additional resonance, r] (1420), has been observed, mainly in proton-antiproton annihilations at rest (451 and in the J/\k radiative decay [44b]. Several interpretations have been proposed for q(l420): The fact that its production in the J/q radiative decay is important has led several authors to propose that 77 (1420) is a O-+ glueball [46]; however, its mass is too small compared to the current estimations, which are above 2 GeV [47]. H. Lipkin 1481 has advocated the possibility that 77(1420) is a ‘giant resonance’ due to the quasi-degeneration of the B member of the 2 ‘So q4 nonet (assuming octetsinglet ideal mixing) with the non-s8 member of the 3 ‘So qq nonet. 77(1420) has often been taken as the Ss isoscalar member of the 2 ‘So nonet, tak-

117

ing into account that the main decay mode known ten years ago was K*R (461. Two recent results allow some of these interpretations to be rejected. First, OB (43~1 confirms the old bubble chamber results (451 that 77 (1420) is observed in protonantiproton annihilations at rest from S states of the protonium [whereas fi (1285) and fl (1420) are produced from P states]. Moreover, OB has shown that the K&r decay is not dominated by K’l?. This final state, which would be favoured if 77 (1440) were an SZIquarkonium, represents only 3% of the K&r decay of 17 (1440). The other result is from CB [49]. It shows that 17 (1420) has an important q1r~ decay: (1420) --) qxn = 0.6 f 0.2 .

7 (1420) + K&/q

This result is in sharp contrast with the branching ratios observed for the 9 (1420) produced in the radiative decay of the J/\k. One may therefore wonder if the 11 (1420) observed in protonantiproton annihilations (which we used to call ‘E’) is identical to the 77 (1420) observed in the radiative decays of the J/\k (‘L’). Another decay mode of the E has been investigated, namely E --+ ~‘IW . Preliminary results were reported pellier QCD’97 conference [50]:

17 (1420) -+ +r/q

at the Mont-

(1420) + 177~ w l/l

.

If these results are confirmed (by CB or OB), they could shed new light on the nature of the E (471, which remains, with the g, one of the most puzzling questions of light-quark meson spectroscopy. REFERENCES Review of Particle Physics, Eur. Phys. J., C3 (1998). E. Klempt, K. Peters, Phys. Lett., B352 (1995) 467. A. Abele et al. (CB), Phys. Lett., B423 (1998) 175. D.R. Thomson et al., Phys. Rev. Lett., 79 (1997) 1630.

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7. 8. 9. 10. 11. 12. 13.

14. 15.

16.

17. 18. 19. 20. 21. 22. 23. 24. 25.

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